Glass containers such as bottles, flasks or jars for the food industries or pharmaceutical industry, generally are produced in automated installations or plants. The production rates of such installations are very high. For example, containers with a unit weight of 100 g are produced at rates of up to 200 units per minute while containers with a unit weight of 900 g are produced at rates of up to 65 units per minute. To assure that contours or shapes, volumes (capacity) and other features of the containers are in accordance with product specifications including final use requirements, such as suitability for automatic bottling (filling and closing) which may require pressure sealing caps, crown corks or stoppers, a very rigid inspection of such critical features is required. Furthermore, the containers must be checked for absence of defects such as cracks, most importantly at the neck and bottom portion of the containers because such defects would increase the breakage hazard or render closing of the containers impossible. The term "crack", here, is intended to include various types of crizzles, splits, checks, fissures, blisters, spikes, jaggers and other defects inside the glass, whether they extend to a glass surface or not, capable of being spotted by deflection of light beams.
Both defects of contours or dimension and crack-type defects at the neck or bottom portions of the containers appear at random. Therefore, spot-checking or random-checking does not provide a sufficient quality control and each container produced must be examined individually. For this purpose, commercial container producing installations of the type mentioned above generally include inspection lines for checking the containers produced.
According to conventional practice, cracks at the neck or bottom portions of glass containers are detected by optical means. For example, in a typical crack-checking apparatus, each container is rotated around its vertical axis at least once, while at least one beam is directed at the article under inspection. For crack detection, the light emanating or being reflected from said container under predetermined angles is surveyed. This method works on the principle that cracks of the type mentioned above in vitreous substances are capable of forming an optical interface or boundary therein. Such a boundary will totally reflect a light beam with an angle of incidence greater than the critical or limiting angle of total reflection. This result is utilized to trigger a sensor for either accepting or rejecting that container.
In U.S. Pat. No. 3,533,704, issued in 1970 to the inventor herein, an inspection method is disclosed for taking advantage of this principle. Another approach is disclosed in U.S. Pat. No. 3,639,067 issued in 1972 to Stephens.
Most cracks are caused by stresses or tensions which result from initial cooling of the glass. While annealing may alleviate stresses it does not necessarily eliminate all cracks. The general direction of such cracks will usually be from the outer glass surface toward the inner surface of the glass container, that is predominantly in a radial direction. In order to detect substantially all such cracks regardless of their position and direction, a crack-checking apparatus generally includes several light emitters and several light sensors. Since the totally reflected light bundles have a width and, concomitantly an intensity, which increases as the angle of impact approaches the critical or limiting angle of total reflection, emission of the light bundle and the sensor or detector preferably are arranged such that the angle of the incident light approaches the limiting angle of total reflection. Further, in order to detect or sense totally reflected light, the incident light bundle and the light receiving part or sensor of the light detector should be in the same plane and be perpendicularly oriented with respect to the plane defined by the crack. It should be noted that the foregoing comments apply particularly to my prior U.S. Pat. No. 3,533,704 referred to above. Others have been successful in orienting light emitters and sensors in other ways for inspecting containers of various configurations. For example, the Stephens U.S. Pat. No. 3,639,067 illustrates a slightly different approach to the concept of inspecting glassware by optical means.
Whichever approach one chooses to follow, the technical problem is to arrange a plurality of light emitters or light sources, suitable for generating such light beams or bundles, and a plurality of coordinated light sensors or detectors under mutual angles which are functionally dependent upon the angles of reflection and refraction, and their positions will depend upon shape, contour and dimension of the containers to be tested. Mechanically, such an arrangement must be quite stable because the machines, and checking installations, are subjected to strong and continuous vibration, and also because it may happen in high speed production and its concurrent high conveying velocities that a container rebounds somewhere from the conveying line and hits the support of the testing devices or the testing devices proper. On the other hand, the arrangement or support should allow quick and reproducible setting or resetting of the testing devices so that upon a change of production from one size or type of container to another, readjustment is possible within a reasonably short time. The same testing apparatus can sometimes be used for continuously checking containers of various vertical heights when the neck or finish is similar to some other container configuration.
Inspection apparatus of various types are known and have, for example, been disclosed in U.S. Pat. No. 2,902,151 issued to Miles in 1959; No. 3,101,848 issued to Uhlig in 1963 and No. 3,249,224 also issued to Uhlig in 1963. These prior art machines do not show or suggest any standardized inspection head design, but instead generally include a number of vertical columns or rods interconnected by means of horizontal rails or cross bars with the optical testing devices mounted either on the rods or the rails by means of bars and pivotable brackets or knuckle joints. Such arrangements can be made to have sufficient mechanical stability but require frequent readjustment and, thus, repeated checking of the setting, because the original setting slowly changes under continuous vibration. Another important disadvantage of such prior art optical installations is that any new setting upon change of production requires highly skilled personnel and is quite time-consuming. For example, a new setting of a prior art checking apparatus typically may require up to ten hours while resetting of the production plant proper normally can be done within about an hour only. Thus, the time now required for a change of container production, be it in size or in type of the containers, will depend essentially upon the time required for setting the test components and, specifically, the crack-checking apparatus.
In order to obviate these problems it has been suggested to use a system of special support rods and pivotable clamps for mounting the test devices, the rods and clamps being provided with scales and circular divisions engraved thereon so that a setting once selected could be repeated or reproduced easily. Practice has shown, however, that such arrangements, while facilitating an approximative setting, still require additional fine setting which again is complicated and time consuming. Also, the engraved scales of the support rods and the circular divisions of the pivot clamps render such mounting devices quite expensive. U.S. Pat. No. 3,085,160 issued to Dahms in 1963 shows such a system. Modern automated plants generally produce glass containers of standardized shapes and dimensions and most commercial production machines have to be capable of producing a certain variety of such container types. Accordingly, it would be desirable to have a means for at least partially replacing prior art mounting and supporting mechanisms such as rods, rails, cross bars and clamps for supporting the testing installations with integrated arrangements in the form of testing heads for fixed or preset adjustment, each testing head being suitable for use in the inspection of a specific container type of a specific group of containers.